The free version of this digital tool is an ideal place to start and may well be plenty to suit your needs in creating short explainer videos (less than 5 mins). It's an ideal way to create short videos to share with students to explain concepts or for students to share with their teachers to explain their online work. By clicking on the extension icon you can choose how much of your screen you'd like to record and then hit the record button to begin your explainer video. Screencastify is a chrome extension which sits in your browser (at the top right hand side of the screen generally) and can be accessed when you are on any webpage. Screencastify: Free Chrome Extension (Paid for version available also)